1. Field of the Invention
This invention relates generally to local area networks (LANs) and more particularly to apparatus and a method for analyzing the performance of the system members coupled to the local area network.
2. Description of the Related Art
For certain local area networks, such as the Carrier Sense Multiple Access/Collision Detect (CSMA/CD) architecture, as defined by the IEEE 802.3, multiplicity of devices can be coupled to a segment (cable) of the local area network. For example, the devices can be coupled to a segment consisting of a coaxial cable segment 500 meters in length. A local area network can include a plurality of segment cables, each segment cable coupled by a repeater unit (to compensate for losses experienced by propagation along the cable) to other segment cables and having up to 1024 system members coupled thereto. The system members are coupled to the coaxial cable by means of a device typically referred to as a tap. The tap is a unit that clamps onto the coaxial cable, pushes aside the braided grounding wire, and forces a small pin into the central conducting element to detect signals transmitted on the conducting element. Referring now to FIG. 1, the typical configuration of a device coupled to the segment cable is shown. The tap and transceiver unit 12 is coupled to the coaxial segment cable 11. The tap portion physically couples to segment cable, while the transceiver portion encodes signals that are applied to the segment cable 11 in the specified local area network format and decodes signals received from the segment cable 11. The network interconnect unit 14 is coupled to the tap and transceiver unit 12 and provides the data link protocols specific to the local area network. The network interconnect unit 14 typically provides power for the trap and transceiver unit 12 through the same conducting leads that carry the signals. The network interconnect unit 14 is typically contained within a data processing system 15, the data processing system typically referred to as a network node.
Data is transferred between local area network system members over at least one segment cable. The data is typically transferred in groups of signals referred to as packets. The packets, in addition to the information conveyed therein, include a plurality of identifying fields such as the source local area network system member and the target local area network member. The presence of the field specifying the source of the data packet in the packet itself is important to the operation of the invention disclosed herein.
A need has therefore been felt for apparatus and for a method that can determine characteristics of system members coupled to a local area network segment cable. Specifically, apparatus and a method are needed that can identify devices that are providing signals having characteristics outside permitted limits and can identify failing system members.